Investigation of thermo-mechanical performance of PCM incorporated Geothermal Energy Pile (PCMinGEEP)

Lead Research Organisation: University of Surrey
Department Name: Civil and Environmental Engineering

Abstract

The latest report of Intergovernmental Panel on Climate Change (IPCC) 'Global warming of 1.5C' emphasises the need for 'rapid and far-reaching' actions now to curb carbon emission to limit global warming and climate change impact. Decarbonising heating is one of the actions which is going to play a key role in reducing carbon emission. The Committee on Climate Change states that insufficient progress has been made towards the low carbon heating homes target that requires immediate attention to meet our carbon budget.

It is well known fact that the ground is warmer compared to air in winter and cooler in summer. Therefore our ancestors build caves and homes underground to protect them against extreme cold/hot weather. Geothermal energy pile (GEEP) basically consists of a pile foundation, heat exchanging loops and a heat pump. Heat exchanging loops are usually made of high density polyethylene pipes and carry heat exchanging fluid (water and/or ethylene glycol). Loops are attached to a reinforcement cage and installed into the concrete pile foundations of a building to extract the shallow ground energy via a heat pump to heat the building during winter. The cycle is reversed during summer when heat is collected from the building and stored in the ground. GEEP can play an important role in decarbonising heating as it utilises the sustainable ground energy available under our feet.

High initial cost remains the main challenge in deploying heat pump technology. In the case of GEEP, the initial cost can be reduced, if the heat capacity of the concrete is improved and loop length can thus be decreased. This can be achieved by incorporating phase change material (PCM) in the concrete. PCM has a peculiar characteristic that it absorbs or releases large amount of energy during phase change (solid to liquid or liquid to solid).

This project aims to develop an innovative solution by combining two technologies GEEP and PCM to obtain more heat energy per unit loop length which would reduce the cost of GEEP significantly. PCM has never been used with GEEP in the past, therefore obvious research questions that come to the mind are (1) how to inject PCM in concrete (2) what would be the effect of PCM on concrete strength and workability (3) how PCM would affect load capacity of GEEP as primary objective of the GEEP is to support structure (4) how much heat energy would be available (5) what would happen to the ground temperature surrounding GEEP (6) how much it would cost (7) whether it would reduce carbon footprint of concrete.

We aim to answer all the above research questions by employing sustainable and environmental friendly PCM and impregnate it in light weight aggregates (LWAs) made with waste material (e.g. fly ash, slag, glass). There are three advantages of using LWAs made from waste: first LWAs will replace natural aggregate in concrete as natural aggregates are carbon intense, second LWAs are porous and light so they can absorb large amount of PCM and reduce the weight of concrete, third reuse the waste. Laboratory scale concrete GEEP will be made with PCM impregnated LWAs and tested under heating and cooling load to investigate thermal (heat transfer) and mechanical (load capacity) performance. Extensive experimental and numerical study will be carried out to design and develop novel PCM incorporated GEEP which can provide renewable ground energy for heating and cooling.

Planned Impact

The PCMinGEEP project is going to be a game changer for heating homes using shallow geothermal energy. The project will have the following noticeable impact on environment, society, technology, engineering, economy and education:

Environmental impact:
Presently most people use fossil fuel (i.e. gas & oil) for heating homes and hot water. We all know how damaging the fossil fuels are to our environment in terms of carbon emissions and global warming. Shallow geothermal energy is sustainable and renewable as it comes from the sun as the earth surface absorbs solar radiation all year round. Use of shallow geothermal energy for heating homes is going to decrease carbon emissions considerably and help us in fighting global warming.
Zero energy buildings remain a dream for Governments around the world. This project will play a significant role in developing zero energy buildings by using geothermal energy.
We propose the use of light weight aggregates (LWAs) made from waste such as fly ash, slag and glass to produce a concrete geothermal energy pile (GEEP). LWAs are going to replace natural aggregates in concrete. The natural aggregates are non-renewable and are carbon intense. LWAs will reduce and recycle the waste and save natural resources for our future generations.

Societal impact:
The majority of people heat homes using gas which poses risk of carbon-monoxide leakage. Everyone understands the danger of carbon-monoxide as it can cause death and brain damage. Use of geothermal energy for heating homes eliminates the use of gas for heating and its risks.
Cold homes can cause long term health issues related to cardiovascular and respiratory system and our national health service (NHS) spends millions of pounds to treat them. This project will benefit people as well as the NHS by delivering renewable heating at low cost in the long term.

Technological impact:
Phase change materials (PCMs) are capable of storing and releasing a large amount of energy in the form of latent heat during the phase change. It will be the first time that the PCMs will be applied to GEEP to extract geothermal energy for heating. This will be a step change for the existing GEEP technology. The project will find suitable PCMs which are environmental friendly and develop a sustainable solution by introducing PCMs in GEEP using LWAs. We will apply for a patent to protect our innovative work and to develop future inventions. The product and technology developed during this project could be extended to other building components such as wall, slab, windows etc. and applied to other fields such as medicine and food.

Engineering Impact:
The project is multi-disciplinary and, hence, it is going to have a significant impact on various engineering disciplines such as heat ventilation air condition (HVAC) engineering, civil engineering, architecture and chemical engineering. In order to realise the impact of the project these engineers will be informed about how GEEP can provide sustainable energy for heating.

Economic impact:
This project will develop new products and methods which will be exploited by setting up a spin-off with the help of our industry partners. We will use our commercialisation and technology transfer team at the University of Surrey to take the product from the laboratory to the market. Currently we do not have any industry producing LWAs using glass waste. Similarly, there are opportunities for producing PCMs in the UK using local products. The project will create new industries and jobs in the field of LWAs, PCMs and concrete piles.

Educational impact:
We are already educating our MSc students at the University of Surrey about GEEP technology and its design. We will share the project outcomes by including them in the course content. One post-doctoral research assistant and a PhD student will be directly working on the project and will learn experimental and numerical techniques related to GEEP.

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